Preparation

Prepare the blueberry swirl first since it will take the longest to cook and fully chill. Combine all the ingredients in a medium sauce pan, stirring well before turning on the heat to break up any possible lumps of starch. Cook over medium heat, stirring periodically, until the mixture comes up to a full boil. Turn down the heat slightly so that it stays at a lively simmer, and cook for 1 minute longer, until thickened.

Remove from the stove, cool to room temperature, and then place in the fridge to chill until cold; about 2 – 3 hours.

Place the margarine and sugar in the bowl of your stand mixer, and cream the two together using the paddle attachment. Once thoroughly beaten and homogeneous, pause the mixer and add in the graham cracker crumbs, ground flaxseeds, salt, cinnamon, and vegan sour cream or yogurt. Starting at the lowest speed, allow the mixer to gently incorporate the newest addition, and continue stirring until the entire mixture is moist will stick together when pressed.

Transfer to your prepared pan and spread it out evenly over the bottom. Press it firmly into a smooth layer, using your hands or the bottom of a flat measuring cup.

Bake for 12 – 15 minutes, until golden brown. Let cool completely before turning the whole cookie sheet out of the pan and onto a cutting board. Use a very sharp knife to slice it cleanly down the middle, forming two equal pieces. Trim away the dark edges so that it measures about 8 inches wide and 5 – 6 inches long.

Line an 8 x 8-inch square baking pan with aluminum foil, and carefully place one of the squares inside, fitting it snugly against three of the four edges. Pull the foil up against the remaining side that comes up slightly short. Place the pan and the remaining square of graham cracker cookie in the fridge.

Meanwhile, the ice cream itself comes together very quickly. Simply pile all of the ingredients into your blender and puree briefly, just until smooth. Blend no longer than necessary to prevent the mixture from warming up.

Pour the ice cream base into your ice cream maker and churn according to the manufacturer’s instructions. Pull out your square baking pan and spoon the soft ice cream on top of the graham cookie sheet inside. Smooth out the ice cream to evenly cover the cookie. Spread the blueberry swirl mixture on top, and use a spatula to swirl both components together. Finally, place the remaining rectangle of graham cracker cookie on top, and press down gently. Immediately move the pan into your freezer and let rest until solidified; at least 8 hours and ideally 12 or more. Slice the large ice cream sandwich into smaller rectangles and enjoy.